1. Field of the Invention
Embodiments of the present invention generally relate to a pad assembly for electrochemical mechanical processing.
2. Description of the Related Art
Electrochemical Mechanical Processing (ECMP) is a technique used to remove conductive materials from a substrate surface by electrochemical dissolution while concurrently polishing the substrate with reduced mechanical abrasion as compared to conventional Chemical Mechanical Polishing (CMP) processes. ECMP systems may generally be adapted for deposition of conductive material on the substrate by reversing the polarity of the bias. Electrochemical dissolution is performed by applying a bias between a cathode and a substrate surface to remove conductive materials from the substrate surface into a surrounding electrolyte. The bias may be applied to the substrate surface by a conductive contact disposed on or through a polishing material upon which the substrate is processed. A mechanical component of the polishing process is performed by providing relative motion between the substrate and the polishing material that enhances the removal of the conductive material from the substrate.
Copper is one material that may be polished using electrochemical mechanical polishing. Typically, copper is polished utilizing a two-step process. In the first step, the bulk of the copper is removed, typically leaving some copper residue on the substrate's surface. The copper residue is then removed in a second, or over-polishing, step.
During electrochemical processing, the copper layer disposed on the substrate is pressed against a polishing surface and is biased relative to an electrode. An electrolyte fluid is disposed between the copper layer and the electrode. The electrolyte completes an electrical circuit between the substrate and the electrode, which assists in the removal of material from the surface of the substrate. As the polishing surface and electrode are consumed during processing a number of substrates, periodic replacement of both the polishing surface and electrode is required, thus necessitating interruption of substrate processing. Therefore, it is desirable to configure the polishing surface, electrode and polishing system in general in a configuration that facilitates quick and efficient replacement of the polishing surface and electrode to minimize process interruptions.
Thus, there is a need for an improved apparatus for electrochemical mechanical processing.